Question: Ben is 18 years older than Tiffany. For the last four years, Ben and Tiffany have been going to the same school. Two years ago, Ben was 4 times older than Tiffany. How old is Ben now?
We can use the given information to write down two equations that describe the ages of Ben and Tiffany. Let Ben's current age be $b$ and Tiffany's current age be $t$ The information in the first sentence can be expressed in the following equation: $b = t + 18$ Two years ago, Ben was $b - 2$ years old, and Tiffany was $t - 2$ years old. The information in the second sentence can be expressed in the following equation: $b - 2 = 4(t - 2)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $b$ , it might be easiest to solve our first equation for $t$ and substitute it into our second equation. Solving our first equation for $t$ , we get: $t = b - 18$ . Substituting this into our second equation, we get the equation: $b - 2 = 4($ $(b - 18)$ $ -$ $ 2)$ which combines the information about $b$ from both of our original equations. Simplifying the right side of this equation, we get: $b - 2 = 4b - 80$ Solving for $b$ , we get: $3 b = 78$ $b = 26$.